/*
 * Copyright 2015 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.agera;

import com.google.agera.Common.StaticProducer;

/**
 * Utility methods for obtaining {@link Merger} instances.
 */
public final class Mergers {
    private static final ObjectsUnequalMerger OBJECTS_UNEQUAL_MERGER = new ObjectsUnequalMerger();

    /**
     * Returns a {@link Merger} that outputs the given {@code value} regardless of the input values.
     *
     * @param value TTo
     * @return Merger<TFirst, TSecond, TTo>
     */
    @NonNull
    public static <TFirst, TSecond, TTo> Merger<TFirst, TSecond, TTo> staticMerger(@NonNull final TTo value) {
        return new StaticProducer<>(value);
    }

    /**
     * Returns a {@link Merger} that outputs the <i>negated</i> result of {@link Object#equals} called
     * on the first input value, using the second input value as the argument of that call.
     *
     * @return Merger<Object, Object, Boolean>
     */
    @NonNull
    public static Merger<Object, Object, Boolean> objectsUnequal() {
        return OBJECTS_UNEQUAL_MERGER;
    }

    private static final class ObjectsUnequalMerger implements Merger<Object, Object, Boolean> {
        @NonNull
        @Override
        public Boolean merge(@NonNull final Object oldValue, @NonNull final Object newValue) {
            return !oldValue.equals(newValue);
        }
    }

    private Mergers() {}
}
